In the field of musical instrument power amplifiers, examples of circuits which deviate from standard "hi-fi" or commercial designs in order to provide specific musical instrument enhancement(s) are rarely found. Most instrument-specific enhancement circuitry is found in the domain of preamplifier circuitry. The musician's power amplifier most often is virtually--or literally--follows one or another of the many commercially available high-fidelity power amplifier designs. Solid state power amplifiers often include peak limiters or compressors when used in musical systems in order to avoid undesirable clipping distortion, but this objective is more nearly the opposite from that of the present invention.
Distorted response (caused by saturation clipping) is often preferred for single-note solo passages, especially in the blues, rock and pop-music idioms. (Creating and enhancing "desirable" distortion characteristics can be a very vital enterprise resulting ultimately in successful artistic careers, and mass sales of recorded material.) Faithful, non-distorted power amplifier characteristics are similarly required for chordal playing plus single note solo passages in other musical styles.
Playing the modern electric guitar yields an "amplified" sensation which is a combination of tactile and musical experiences. The musician's fingers touch the instrument's mechanically active element--the string--both adjusting its length (fretting) and providing its vibrational energy (plucking and strumming). The mental "feedback look" between the physical sensation of "playing" and the auditory experience of "playing" is one of great intimacy for the accomplished musician and is all the more heightened by the inclusion of sensitive, dynamic amplification. It is precisely here, in coalition of tactile and auditory sensations that the present invention solves a longstanding problem of offering enhanced performance and satisfaction to the musician and to the audience which is both "giving and forgiving".
For the non-musician who may have trouble perceiving the virtues of an amplifier that is both "giving and forgiving," picture, for example, a pair of snow skis. Skis are certainly well known and in use, and from outside appearances, one looks very much like any other. Yet untold hours of development would have been invested in discovering and producing superior skis that have the "right amount" of "dynamic springiness" to be highly responsive at slow speeds and noticeably forgiving at high speeds.
In previous pentode audio power amplifiers, good voltage regulation of the screen grid supply has been relatively easy to obtain and has always been deemed a virtue in amplifier design. Often the screen grid D. C. supply is maintained at a constant voltage relative to ground via a dedicated voltage regulator or by a high current voltage divider that is relatively immune to fluxuating screen current demands. Another method very common to musical instrument amplifiers is to derive the screen voltage from the main B+ point (center tap of output transformer) through a filter resistor or a filter choke, either one of which has a very low D. C. resistance. Thus the screen supply is held a few volts lower than the plate supply and this small voltage drop remains practically constant under fluxuating load demands from the plate. Changes in the screen voltage occur virtually simultaneously with changes in the plate voltage (at least in "musically significant" measures of time) because high current demands from the plate actually drain voltage stored in the screen decoupling capacitor as well as the main B+ filter, through the small D. C. resistance between them. And in the version of screen supply known as "ulta-linear" the screen voltage is derived from taps on the primary winding of the output transformer, where again it fluxuates simultaneously with and thereby tracks the D. C. plate voltage.